I. Field of the Invention
This invention relates to ultrasonic transducers in general and more particularly to a biplane phased array ultrasonic transducer arrangement having effectively two arrays of ultrasonic oscillators and electrode patterns on opposite major faces of a piezoelectric material, each array consisting of several acoustically separated transducer elements which are electrically controlled to operate independently. The biplane phased array permits the real time imaging of two planar sectors which can be at any relative angle to another.
II. Description of the Prior Art
Modern ultrasound scanners employ phased array transducers to accomplish electronic steering and focussing of the acoustic beam in a planar sector. These arrays are commonly fabricated from a plate of piezoelectric ceramic by cutting the plate into narrow plank shaped elements. In order to obtain a wide angular response free of grating lobes, the center-to-center element spacing is approximately a half wavelength of sound in tissue at the center frequency.
A novel device combining two orthogonal phased arrays for real time imaging of two orthogonal sectors is disclosed in U.S. patent application Ser. No. 749,613, filed June 27, 1985 entitled "A Biplane Phased Array for Ultrasonic Medical Imaging", Pieter 't Hoen inventor, and assigned to the assignee of the present application, which application is incorporated herein by reference. This application discloses a biplane phased array fabricated by putting an electrode surface on each major surface of a slice of a composite piezoelectric material and scoring the electrode surfaces such that the scoring on one side is at an angle with the scoring on the other side and the scoring does not penetrate the composite material. Appropriate electrical connections are made such that all electrode elements on one electrode surface are grounded and the phasing is performed with remaining free electrodes to image, according to the phased array principle in one direction, and alternately all the electrode elements on the other electrode surface are grounded so that the phasing is performed with the free electrodes on the first side to image in a second direction. The array of transducers is capped on one side by a mechanical lens.
Such a biplane phased array is especially useful in cardiac scanning. Simultaneous horizontal and vertical cross sections of the heart will allow the physician to evaluate more effectively the functioning of the heart. The demonstration of low cross talk in composite piezoelectric arrays suggested the application of composite materials to the design of a biplane phased array.